He made his first team – and Série A – debut on 22 August 2004, coming on as a second half substitute for Sandro Hiroshi in a 1–1 home draw against Vasco da Gama.

[4] While on loan, Willian scored eight goals during the year's Série B, being the club's top goalscorer as his side avoided relegation.

[12] Mainly used as a substitute during the Campeonato Paulista, he became a regular starter for the club during the year's Brasileirão; he scored a double in a 2–0 home win against Fluminense on 12 June.

On 2 July 2012, Willian moved abroad, signing for Ukrainian Premier League club FC Metalist Kharkiv.

[15] Willian made his continental debut on 23 August 2012, starting in a 2–0 away win against FC Dinamo București in the UEFA Europa League.

On 14 July 2013, Willian signed a one-year loan deal with Cruzeiro, with Diego Souza moving permanently in the opposite direction.

[17] Roughly one year later, he was bought outright for a fee of €3.5 million;[18] he also appeared regularly as his side achieved back-to-back Brasileirão titles in 2013 and 2014.

[25] Mainly a backup to Germán Cano, Willian won two consecutive Carioca titles with the club, but featured very rarely in the 2023 campaign.